Photographic printing apparatus



EMMINEB REFERENCE P9998,

FIPGZIZ Feb. 13, 1934.

R. N. CARTER rnowoemxrmc rmmmp APPARATUS Filed July 30, 1932 Patented Feb. 13, 1934,

rno'rocmmc ram'rmo msasros Bella N. Carter, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York Application July 30, 1932. Serial No. 628,747

' Claims. (CI. 88-24) My invention relates to photography and more particularly to apparatus for controlling automatically the exposure given in printing a photographic record.

5 In printing sensitized layers from photographic records varying in average density it is generally desirable to give each layer a constant exposure so that upon being developed a printed product of substantially constant density will be produced.

The reciprocity law teaches that a constant printed product will be obtained if the product of the printing light intensity and the time it is permitted to fall on the layer is held constant. In practice, however, it the intensity of the light falling on the record is held constant and the time of exposure varied in accordance with the average density of the record it is found in printing records differing greatly in density that the developed layer will vary from the'desired constant density due to what is generally called failure of the law of reciprocity. In order to compensate tor the failure or this law it is necessary to progressively increase the quantum of light talling on the sensitized layer as the average density of the record increases.

It is an object or my invention to provide a printing apparatus which will automatically increase the quantum of printing light as the average transmission of the record decreases. Another object 01' my invention is to provide an automatic printer in which the exposure time for records differing in density increases at a more rapid rate than called for by the reciprocity law.

In accordance with my invention the timing mechanism comprises two parts whose movements are governed in accordance with the intensity oi. the printing light 1. e., the light transmitted by the record, and the summation oi the movements of these two partsdetermine the exposure period.

Other objects and advantages or my invention will appear from the following description taken in connection with the accompanying drawing in which Fig. 1 'shows a circuit organization whereby my invention may be carried into effect, the invention in this instance being applied to a contact printer. Fig. 2 shows a modified circuit arrangement applied to a printer 0! the projecting or argin tim The essential parts as shown in Fig. 1 include suitable means for holding a photographic record and a sensitized layer and may comprise two plates 10 and 11 of glass or other transparent material hinged together so that one of the plates is movable and may serve as a platen. A lamp 12 for furnishing a printing light is adapted to be connected to a source of supply 13 through leads 14 and a switch 15. The switch 15 is normally held in open position by the tension of a spring 16 and is adapted to be held in closed position by 00 the armature 17 of a coil 18. When the coil 18 is energized by a battery 19 as hereinafter described the armature 17 is withdrawn and the spring 16 opens the switch 15.

A light sensitive element 20 positioned to receive light transmitted by the record and layer during printing controls the energization of a coil 21 mounted in a magnetic field set up by magnets 22 and which rotates at an angular speed corresponding to its energization. The coil 21 T0 carries a vane 23 which forms a moving contact arm and is adapted to engage another contact 24 to complete the circuit through the battery 19 and the coil 18. The contact 24 is also movable and is adapted to be rotated at a fixed angular speed in any suitable manner as by a coil 25 mounted in a magnetic field set up by magnets 26 and energized a desired amount by adjustment of the taps 2''! on a rheostat 28 connected across the leads 14. It is to be noted that the coil 25 will be energized only when the lamp 12 is energized.

In the operation oi the device when the switch 15 is closed the lamp 12 is energized to start the exposure and the coil 25 together, with its contact arm 24 begins to rotate at a relatively slowspeed in a counter clockwise direction. The light sensitive element 20 is activated and its response causes the coil 21'and its contact vane 23 to rotate in a clockwise direction with an angular speed corresponding to the density of the negative being printed. Alter a time interval dependent upon the density of the negative the vane 23 will overtake and engage the contact arm 24 and close the circuit through the battery 19 and 96 the coil 18. The closing of this circuit causes the removal Q! the armature 17 from latching position and the spring 16 opens the switch 15 to dis continue the exposure.

The energization of the coil 25 is so adjusted 100 -"that the angular speed of the contact arm 24 is the scope of pended claims constant. However, the movement of the contact arm 24 increases the length of the path the vane 23 must travel to terminate the exposure and it will be obvious that the slower the vane 5 23 moves the longer its path will become. In

other words, the product of the printing intensity and the time is progressively increased as --the intensity decreases and with the proper adjustment of the constant speed contact 24 this increased exposure will compensate for the failure oi the law of reciprocity and prints of uniform density will be obtained.

While I have shown the constant speed contact as being rotated by a motor element of the damped coil type obviously it may be rotated or moved by any other suitable means.

In Fig. 2 I have shown a modified form of exposure control applied to a printer of the projection type in which a condenser lens 30 concentrates the light from the lamp 12 onto the negative 31 and a projection lens 32 images the negative 31 on the sensitized layer or positive 33. A partially transmitting and reflecting member 34, which may be of celluloid, is positioned in the path of the light between the negative 31 and the positive 33 and serves to reflect a fixed portion of the light transmitted by the negative 31 onto the light sensitive element 20. The response of the element 20 energizes the damped coil 21 to rotate the contact vane 23 as described in connection with Fig. 1. The path of the vane 23 is determined by the position of a contact arm 35 carried by an indicating meter coil 36 which is also energized by the r sponse of the light sen- 35 sitive element 20. A variable resistance 37 is connected in series with the damped coil 21 for adjusting the relative responses of the two coils 21 and 36 carrying the movable contacts 23 and 35.

In the operation of the device as shown in Fig.

40 2 when the exposure is started by closing the switch 15 the cell 20 is activated and the indicating meter coil 36 moves the contact arm 35 toward the contact vane 23 until it assumes a position corresponding to the cells response.

Simultaneously therewith the coil 21 is energized and rotates the contact vane 23 toward the contact arm 35 at an angular speed corresponding to the response of the cell 20. After an interval of time depending upon the position of the arm 85 and the speed of rotation of the vane 23 the two contacts close the circuit through the battery 19 and the coil 18, and the armature'l'l is attracted to permit the switch 15 to open, thereby terminating the exposure.

1n the arrangement just described the arm 35 of the indicating meter coil 36 functions to lengthen the path of the contact vane 23 as the intensity of the printing light decreases and compensates for the failure of the law of reciprocity 3c Pas does the apparatus described in connection with Fig. 1.

While I have illustrated my invention as applied to printers in which the exposure is controlled by switching on and on the printing lamp 12 it will be understood that the exposure may be controlled in known in the invention will sons skilled any other suitable manner well art. Various modifications of my readily uggest themselves to perin the art without departing from my invention as forth in the apmotor element and the indicating element in ac- WhatIclaimasnewanddesiretosecureby Letters Patent of the United States is:--

1. An apparatus-for the automatic control of exposure in photographic printing, exposure terminating means, a light sensitive element, means energized by said element for actuating said exposure terminating means including an electromagnetic coil adapted to rotate at a speed proportional to its energization and means for varying the length of the path of said coil in accordance with the response of said light sensitive element.

2. Photographic apparatus including means for holding a sensitized layer in position to be exposed to light, an electric motor element adapted to rotate at a speed proportional to its energization, an electric indicating element adapted to move a pointer to a position corresponding to its energization, means for energizing the cordance with the intensity of the exposing light falling on said sensitized layer and means operative to discontinue the exposure when said motor element has rotated through an angle determined by the position of the pointer of said indicating element.

3. In photographic printing apparatus, a source of light for illuminating a photographic record to be printed, means for supporting a sensitized layer in position to be exposed to light transmitted by the photographic record, a light sensitive element responsive to a definite proportion of the light transmitted by said record, a pair of relatively movable contacts, means for moving one of said contacts at a rate corresponding to 113 the response of said element and means for adlusting the position or the other of said contacts in accordance with the response of said element, and a control circuit adapted to be completed by the engagement of said movable contacts and operative to discontinue the exposure of said sensitized layer.

4. Photographic printing apparatus including means for supporting a sensitized layer in position to be exposed to light transmitted by a photographic record, means for terminating the exposure, a pair of cooperating contacts adapted u'pon engagement to actuate the exposure terminating means, means for moving one of said contacts toward the other said contact at a gig velocity corresponding to the average intensity of the light transmitted by the photographic rec- 0rd and means for adjusting the position of the said other contact in accordance with the average intensity of the light transmitted by the photographic record.

-5. Photographic printing apparatus including means for supporting a sensitized layer in pomtiontobeexposedtolighttransmittedbyaphotographic record, means for terminating the exposure, means movable at a rate corresponding to the average intensity of the light transmitted by the record and through a path from a predetermined position to a position at which the exposure terminatingmeansisactuatedand means for varying the length of the path between said positions as an inverse function of the rate of movement of said movable means.

ROLLA N. CARTER. 

